Old-fashioned gerrymandering sometimes worked that way. You'd have incumbents- in both parties- try and use the gerrymander to keep their individual seats, for

Old-fashioned gerrymandering sometimes worked that way. You'd have incumbents- in both parties- try and use the gerrymander to keep their individual seats, for personal political reasons. Party bosses made sure that their own seats were uncontestable, because they had power over the process. Sometimes this would cross party lines (you, party A boss, give me a safe seat, I'll vote to give you a safe seat, we'll both be happy). The way it works now is that you create a perfectly safe seat for the other party in exchange for many more fairly comfortable seats for your own party. The maps are not drawn up to make individual incumbents happy, but to maximize party power. The fairly comfortable seats may still be "safe" in normal elections- they're not 100% a sure thing, but they're not particularly competitive and elections can be reliably fought and won cycle after cycle. You can't just not campaign, but the other side has one hand tied behind their backs, so as long as you have a competent campaign and no sex scandals, you're fine. Whether that's the sort of "safe seat" people are talking about I couldn't say.